Method for decolorization of alkyleneamines

Abstract: Color-containing alkyleneamines, having color numbers of up to 100 PtCo or higher, can be treated with inorganic solid acidic catalysts. Inorganic support materials having bonded inorganic acid functionalities may be used as the inorganic solid acidic catalysts. In the presence of water, these inorganic solid acidic catalysts produce decolorized alkyleneamines having color numbers of 20 PtCo or less. The process of decolorization can be carried out in batch or continuous mode processes thus providing low cost, high quality and high purity end products.

Description: The present invention relates to processes for decolorizing alkyleneamines, and more particularly, to both batch and continuous processes for producing alkyleneamines having improved color characteristics by treatment with solid acidic catalyst. Price and purity are important characteristics of a chemical's marketability to a potential customer. During industrial processes used to produce various chemicals, impurities often enter the processes and manifest themselves in the form of color contamination. The sources of this color contamination may be metals and metal compounds from the catalysts or equipment used in the processes, or conjugated organic compounds which are formed during the processes. Since the mechanism by which these color contaminants are formed varies from process to process, the decolorization process normally acts by a mechanism which depends on the color source. It is well known that alkyleneamines, particularly the higher polyamines, become discolored during their preparation which generally reduces their commercial value. Various procedures have been used commercially or suggested for decolorizing or otherwise improving the color of these compounds including, for example, treating with hydrogen chloride or amine hydrochlorides as disclosed in JA-119902, UK Pat. No. 1,351,050; treatment with activated carbon, acid treated clays or acidic zeolites at elevated temperatures (about 200°C) as disclosed in U.S. Pat. Nos. 3,723,529 and 4,737,243; and treatment with a sulfonic acid ion exchange resin as disclosed in U.S. Pat. No. 4,731,165. In each of these procedures, distillation is generally a final step needed to achieve the desired color, and neutralization of residues, handling and disposal of acids, or reactivation of the treatment medium require special apparatus which complicate the processes. U.S. Pat. No. 4,570,019 discloses a process which may be run continuously for producing polyalkylene polyamines having improved color characteristics which comprises treating discolored polyethylene polyamines with polyethylene polyamine hydrochloride in the presence of water at elevated temperatures, thus eliminating extra handling steps described in the processes above. The above patents confirm the need for methods of improving the color characteristics of alkyleneamines. While some of the processes such as the use of solid adsorbents results in improved color, such processes are not entirely suitable for large scale decolorization and require labor intensive steps for recovery of the desired product adding expense to the process in terms of time of treatment, equipment costs, and disposal of byproducts. Other methods, such as hydrogenation of color impurities require expensive Raney nickel which must be replaced on a regular schedule. Hydrogenation systems also require special equipment for hydrogen supply, mixing and, after reduction, filtration to remove the Raney nickel, since distillation in the presence of Raney nickel tends to generate color and deactivate the catalyst. The need exists for an inexpensive easily operated process of producing alkyleneamines having reduced color. The present invention provides a method of producing alkyleneamines having a reduced colour comprising contacting, in the presence of water, color-containing alkyleneamines with a solid acidic catalyst comprising an aluminum oxide or zirconium oxide support material having a bonded inorganic acid functionality comprising chloride, fluoride or sulfate ions. The present invention also provides a method of producing triethylenetetramine having a reduced color comprising contacting, in the presence of water, color containing triethylenetetramine with a solid acidic catalyst comprising an alumina support material having a bonded fluoride acid functionality, under conditions effective to reduce the color of the triethylenetetramine to a color number of 50 PtCo or less. Preferably the decolorization step is carried out under pressure high enough to maintain the water in the liquid phase. The heterogeneous catalysts used in accordance with the present invention advantageously provide versatility in allowing both batch and continuous processing of the color-containing alkyleneamines. The process may readily be incorporated into typical manufacturing facilities, providing low cost, high quality and high purity end products. The method of the invention may effectively treat color-containing alkyleneamines with colors up to a Platinum-Cobalt (PtCo) number of 100 or higher to obtain products with reduced color numbers of about 20 PtCo or less. The discolored alkyleneamines to which the present invention relates can be prepared by any of the processes well known in the art such as where a crude mixture is produced and then subjected to refining procedures where desired individual components or mixtures thereof are separated and recovered. The products recovered by the various refining or separation processes are, in general, discolored, having PtCo numbers ranging from up to 700 or greater, as determined using ASTM Method 1209 "Color of Clear Liquids (Platinum-Cobalt Scale)." In addition, alkyleneamines which may have been treated previously by other known decolorization methods, some of which may have lower color numbers initially, upon storage become discolored due to increases in storage temperatures, exposure to air or metal contamination from the storage container. Preferred embodiments of the invention will now be described. Color impurities found in alkyleneamines may be removed by contacting color-containing alkyleneamines with solid acidic catalysts. Suitable solid acidic catalysts for use in the practice of the invention include compounds prepared by treating an inorganic aluminum oxide or zirconium oxide support material with inorganic acids, or compounds which provide inorganic acid functionalities in situ, which bond to the support material. Mixed metal oxide support materials may also be used in preparing solid acidic catalysts and include for example, TiO 2 /Al 2 O 3 , SiO 2 /Al 2 O 3 and ZrO 2 /Al 2 O 3 . Aluminum oxides, in particular activated aluminas, comprise a preferred class of supports, and are a series of partially hydroxylated aluminum oxides. In general, as a hydrous alumina precursor is heated, hydroxyl groups are driven off leaving a porous solid structure of activated alumina. This controlled heating or calcining process results in a series of transitional aluminas or activated aluminas. Of the activated aluminas described above, gamma aluminas are preferred since the higher surface area, generally 100-300 m 2 /gm or higher, provides increased sites for acidity. The term "support," as used herein and in the claims, means a solid structure which does not unduly adversely affect the catalytic properties of the catalyst and is at least as stable as the catalyst to the reaction medium. Although some of the support materials used may have acidic characteristics, such as silica-aluminas, it has been found that these types of acidic support materials alone are not sufficient to decolorize alkyleneamines, and instead may contribute to the formation of color bodies when they are not part of the solid acid catalyst structure of the present invention. The solid acidic catalyst is prepared by treating the inorganic support material with inorganic acids, or compounds which provide inorganic acid functionalities in situ, which bond to the support material. The sources of acidity are compounds which provide fluoride, chloride or sulfate ions capable of bonding to the inorganic support material. For example, hydrogen fluoride, ammonium bifluoride, sulfuric acid and hydrochloric acid may be used to provide the inorganic acid functionalities used to produce the solid acidic catalysts. A most preferred source of acidity is ammonium bifluoride. It is believed that it is the high electronegativity of the fluoride ion which provides a stable, reproducible catalyst which does not deleteriously leach when contacted with aqueous amines. Numerous conventional methods of vapor-phase fluorination and impregnation exists for fluorinating support materials such as metal oxides. In one type of vapor-phase fluorination, the metal oxide is maintained in contact with vapors of fluorine-containing compounds such as F 2 , HF, BF 3 , SbF 5 , NH 4 F, CF 4 , CHF 3 , CH 2 F 2 , CF 3 COOH, CF 3 OH, CF 3 OCF 3 , CF 3 CH 2 OH, SF 6 , SO 2 F 2 or SOF 2 at an elevated temperature, usually at a temperature between 100° and 500°C. Another method of preparing fluorinated solid acidic catalysts may be by impregnation, carried out by saturating the catalyst, usually at room temperature, with an aqueous solution containing an appropriate amount of a compound such as HF, BF 3 , HBF 4 , NH 4 F, NH 4 HF 2 , NH 4 BF or NH 4 SiF 6 . The impregnated catalyst may then be dried at 100°C in vacuum and calcined at higher temperatures ranging from 300°C to 700°C. When treating color-containing alkyleneamines, the amount of catalyst used depends on the concentration and strength of the acid functionality. Generally in a batch mode operation, from 0.1 to 30 percent by weight of the solid acidic catalyst is used based on the weight of material to be treated. For example, when using an alumina treated support containing 3 to 8 percent by weight of fluoride, the amount of catalyst used is preferably 10 to 15 percent by weight of the material to be treated. It is believed that higher acid concentrations and strengths facilitate the rate of decolorization. However, extensive fluorination may be regressive due to a decrease in available surface area, resulting in lower acid strength (i.e. number of Brönsted sites) above the 10% level of fluorination. Thus, the useful inorganic acid concentrations are from 0.1% to 10%, preferably 1% to 6%, and more preferably 4 to 6% of the weight of the support material The acid concentration and strength may be determined by methods known in the art such as non-aqueous amine titration (Hammett and arylmethanol indicators), infrared spectroscopy, differential thermal analysis and gaseous adsorption. In addition, methods such as ion chromatography or specific ion electrode methods provide a means of analyzing acid solutions before and after contact with the support material to determine acid concentration on the final catalyst. Increased surface area of the catalyst may aid in increasing activity of the catalyst relative to fluoride content. Thus, a preferred catalyst structure comprises an inorganic support material having a surface area from 50 m 2 /gm to 340 m 2 /gm or greater and an inorganic acid concentration of from 4% to 6%. Without intending to be bound by any particular theory, it is believed that in the presence of water, strong protonic acid sites exist on solid acidic catalysts such as fluorinated alumina which may not have been observed on untreated aluminas. The amount of water present is generally in the range of 1 to 10 percent, preferably 3 to 8 percent and most preferably 4 to 6 percent by weight of the material to be decolorized. The above described solid acidic catalysts may reduce color during initial use without water, however, the degree of color reduction and stability of the decolorized product is less and the process may not be adaptable for continuous use processes. Further, anhydrous processes may contribute to deactivation of the catalyst due to the accumulation of heavy byproducts which may form during the color removal step. The process may be run over a wide ranges of temperatures of generably from 150° to 250°C. Preferably, the temperature range is from 190° to 220°C, and most preferably from 205° to 210°C. The pressure of the system should be high enough to assure retention of water in the liquid phase, and is normally in the range of 6.9 to 690 kPa gauge (1-100 psig), more preferably 140 to 520 kPa gauge (20-75 psig), and most preferably 340 to 450 kPa gauge (50-65 psig). In a typical embodiment, the process of the present invention may be carried out in both batch and continuous modes. In the batch mode, treated product is discharged and fresh product, to be treated, is added. The catalyst may conveniently be maintained in the reactor by use of a basket made of porous screens. In a batch mode operation, the use of agitation may be beneficial in improving catalyst efficiency. Typical means of agitation include the use of mechanical stirrers at speeds ranging from 400 to 1200 rpm. In a continuous mode of operation, a fixed catalyst bed may be used and product to be treated pumped through the bed. In such a continuous process, water is typically introduced as makeup and normal distillation is used to provide low color and color stable products. The amount of catalyst used depends on the design of the process equipment, acid concentration and strength, and process conditions, as is known in the art. Although the mechanism of decolorization is not completely understood, it is believed that during a continuous process, color formers are destroyed during the process and become light fragments which are removed during distillation or heavy fragments which go out with the residue stream. The color-containing alkyleneamines should be in contact with the solid acidic catalyst for a time sufficient to produce a decolorized product. Typically, the residence time for either batch or continuous modes of operation may be up to about 8 hours, preferably 4 to 6, and most preferably 4 to 5 hours. The length of time for decolorization depends on the acid concentration and strength of the catalyst, temperature, and amount of water present in the system as illustrated by the following Examples. EXAMPLES The following Examples show the decolorization of an alkyleneamine, triethylenetetramine (TETA), using the process of the present invention. The original untreated crude TETA has a color of 131 PtCo. Example 1 - Preparation of 4% Aluminum Fluoride Catalyst A 200 gram sample of spherical alumina (A-202) having a surface area of 340 m 2 /g, obtained from LaRoche Chemical Company, is mixed with an aqueous solution containing 250 grams water and 15.12 grams of 98% pure ammonium bifluoride (Aldrich Chemical Co.) at ambient temperature for one hour. The fluoride content of the final catalyst is determined by analyzing both the starting solution and the final supernatant solution using ion chromatography. The original solution assayed 3.71 percent fluoride ion and the final supernatant solution assayed 0.5 percent fluoride ion, yielding a 4% aluminum fluoride catalyst. The catalyst is dried at 100°C in vacuum and calcined for 4 hours at 500°C in air prior to use. Examples 2 and 3 were run using an autoclave equipped with an agitator, nitrogen pressure regulator and temperature controller. Distillation equipment consisted of a 5 tray Oldershaw column having 2.54 cm (1 inch) tray spacings, equipped with a distillation head. Example 2 - Control TETA, 400 grams, is charged to the distillation equipment described above. A first distillate fraction of 26 grams is removed at a head temperature of 128°C, pressure of 4 mm Hg and a reflux ratio of five to one. A second distillate fraction, 301 grams untreated TETA, is removed at 135°C, pressure of 4 mm Hg and a reflux ratio of one to one. The second distillate fraction of untreated TETA has a color of 433 PtCo. Example 3 - Color Stabilization of Crude TETA A total of 600 grams of TETA and 30 grams of water are charged to the autoclave reaction equipment described above containing 60 grams of catalyst prepared in Example 1. The autoclave system was purged with nitrogen and pressurized to 379 kPa gauge (55 psig). The agitator was adjusted to between 400 and 600 rpm and the autoclave heated to 205° - 207°C for 4 hours at a regulated pressure of 379 kPa (55 psig). The reactor contents were cooled to 25°C. After cooling, the TETA-water mixture is removed from the autoclave and fractionated in the distillation equipment. At first distillate fraction of 49.3 grams is removed at a head temperature of 131°C, 4 mm Hg and a reflux ratio of five to one. The second distillate fraction, 448.2 grams treated TETA, is removed at a head temperature of 137°C, 4 mm Hg with a reflux ratio of one or one. The color of the treated TETA is 204 PtCo. The experimental procedure is repeated using a 60 grams of a second fluorinated alumina catalyst prepared by the process of Example 1 except calcined at 600°C. The treated TETA distillate, 458.5 grams, has a color of 202 PtCo. Example 4 - Additional Treatment of TETA The distillate fractions from Example 3 (497.5 grams total) are combined and again treated in the autoclave with 5% water and 60 grams of a fluorinated alumina catalyst (6%) which has been calcined at 600°C. Fractional distillation of the treated TETA using the column described above results in a TETA distillate fraction, 376 grams, having a color of 69 PtCo. A sample of untreated refined TETA having an initial PtCo color of 87.5 was used in the following Examples. Example 5 - Control TETA, 231 grams, is fractionated using the distillation equipment of Example 2. The second distillate fraction, 186 grams untreated TETA, is removed at 135°C, 4 mm Hg, and has a color of 185.9 PtCo. Example 6 - Decolorization of Refined TETA TETA, 600 grams, and 30 grams of water are charged to the autoclave equipment of Example 3, containing 60 grams of a 4% aluminum fluoride catalyst prepared by the procedure of Example 1. The autoclave is operated at 205-207°C for 4 hours with 1200 rpm agitation. After cooling, the treated TETA is fractionated in the distillation equipment to yield a second distillate fraction, 506 grams treated TETA, having a color of 44.4 PtCo.

Claims: A method of producing alkyleneamines having a reduced color comprising contacting, in the presence of water, color-containing alkyleneamines with a solid acidic catalyst comprising an aluminum oxide or zirconium oxide support material having a bonded inorganic acid functionality comprising chloride, fluoride or sulfate ions. A method as claimed in claim 1 wherein the inorganic support material is gamma alumina. A method as claimed in claim 1 or 2 wherein the inorganic support material has a surface area greater than 100 m 2 /g. A method as claimed in any one of the preceding claims wherein the inorganic acid functionality is provided by hydrogen fluoride, ammonium bifluoride, sulfuric acid or hydrochloric acid. A method as claimed in any one of the preceding claims wherein the inorganic acid functionality is in a concentration ranging from 0.1 to 10 percent by weight of the support material. A method as claimed in any one of the preceding claims wherein the solid acidic catalyst has been calcined at a temperature of from 300°C to 700°C. A method as claimed in any one of the preceding claims wherein water is present in a concentration of from 1 to 10 percent by weight of the alkyleneamine. A method of producing triethylenetetramine having a reduced color comprising contacting, in the presence of water, color containing triethylenetetramine with a solid acidic catalyst comprising an alumina support material having a bonded fluoride acid functionality, under conditions effective to reduce the color of the triethylenetetramine to a color number of 50 PtCo or less.

Inventors: GIBSON CHARLES ARNOLD, GIBSON, CHARLES ARNOLD
Applicants: UNION CARBIDE CHEM PLASTIC, UNION CARBIDE CHEMICALS & PLASTICS TECHNOLOGY CORPORATION
Application year: 1994
Main classification: C07C209
IPC codes: C07C209